Glossary · Chemistry
Procyanidin
Also written condensed tannin, proanthocyanidin. Each is a name for the same thing, which is why none of them has an entry of its own.
Definition
A chain of flavan-3-ol units — mainly epicatechin, with catechin as a terminal unit — and the principal tannin of cider apples. Chain length determines whether it tastes bitter or astringent.
- Subject
- Chemistry
- Also written
- condensed tannin, proanthocyanidin
In more detail
Short procyanidins of two to four units are perceived chiefly as bitter. As the mean degree of polymerisation rises, bitterness falls and astringency rises, because longer molecules cross-link salivary proteins more effectively and precipitate them. Bittersweet cider apples are distinguished not only by having more procyanidin than dessert apples but by having longer chains.
Procyanidins continue to change after fermentation, polymerising and combining with other molecules, which is why the astringency of a young tannic cider softens with maturation without any of the tannin being removed.
Where this is covered properly
The glossary defines; these pages explain. Each is described in its own words.
Chemistry
Procyanidins
The condensed tannins of cider fruit, whose chain length — not their quantity — decides whether the mouth registers bitterness or astringency.
Chemistry
Epicatechin
The flavan-3-ol that apple procyanidins are almost entirely built from, and the most bitter of the phenolic monomers a cider contains.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Chemistry
Tannin
In cider usage, the phenolic material responsible for bitterness and astringency, principally condensed tannins — procyanidins — built from catechin and epicatechin units.
Chemistry
Oligomer
A molecule built from a small number of repeating units. Oligomeric procyanidins — roughly two to about ten flavan-3-ol units — are the fraction of cider tannin perceived mainly as bitterness.
Chemistry
Polymer
A molecule built from many repeating units. Polymeric procyanidins, long chains of flavan-3-ols, bind salivary proteins efficiently and are the fraction of cider tannin perceived as astringency rather than bitterness.
Chemistry
Mean degree of polymerisation
The average number of monomer units in the procyanidin chains of a sample. It is the analytical figure that predicts whether a fruit’s tannin will read as bitter or as astringent.
Sensory
Astringency
A tactile sensation of drying, roughening and puckering in the mouth, caused by tannins binding and precipitating the proteins that lubricate the oral surfaces. It is a feeling, not a taste.
Sensory
Bitterness
One of the basic tastes, detected by receptors chiefly on the posterior tongue. In cider it comes principally from short-chain procyanidins and from certain phenolic acids.
Where to go next
- Cider glossary — The whole vocabulary, by subject and A–Z.
- Comparisons — Terms that are only really clear when set against the thing they are not.
- Search — Finds terms by their aliases and by their spellings in other languages.
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
Institut national de recherche pour l’agriculture, l’alimentation et l’environnement (INRAE)
INRAE · research institute · retrieved 2026-08-24
French national agricultural research. Its Angers programme produced much of the published work on apple procyanidin chain length and on the relationship between polymer size, bitterness and astringency.
Peer-reviewed literature on apple phenolics and cider sensory perception
Various journals · peer-reviewed literature · registered as competent for this subject
Registered as a class rather than as one paper, because the mechanisms CiderHQ describes — tannin chain length driving the split between bitterness and astringency, salivary protein precipitation, enzymatic browning — are established across many studies rather than resting on any single one. Individual papers are cited where a specific number is quoted.